An arrayed-waveguide grating (AWG) router as an optical multiplexer/demultiplexer (MUX/DEMUX) is a commonly used device in a dense wavelength division multiplexing (DWDM) network. For high-channel count (e.g., greater than 16 channels) MUX/DEMUX applications, AWG devices can generally perform in a satisfactory manner technologically and economically.
An AWG device typically includes a pair of star couplers (at the input and output) and a waveguide array. In conventional AWG designs, due to limitations of standard fabrication techniques for planar lightwave circuits (PLCs) that make formation of infinitely sharp corners/edges difficult, gaps are formed between waveguides. These gaps are present at an interface between a slab waveguide portion of a star coupler and the waveguide array. Widths of these gaps are determined by a maximum aspect ratio associated with, and also limited by, a particular etching and deposition/re-flow process.
When an optical wavefront propagates through the interface, a portion of the power of the optical wavefront is scattered by the gaps into areas between arrayed waveguides. This causes some of the propagating optical wave(s) to become unguided. Scattering loss at the interface is one of the major losses of an AWG device. The gaps also increase diffraction loss at the output star coupler, where more power is transferred to undesirable diffraction orders.
A current method to reduce these losses is to design AWG devices where the gap width between arrayed waveguides is decreased. However, to fabricate such AWG devices, a significantly better etching process and a longer cladding deposition/re-flow process are needed. This greatly increases production costs. Moreover in conventional designs, the output power from the AWG device is non-uniform (e.g., outer channels/waveguides have higher losses than center channels/waveguides), and therefore, only the center portion of the waveguide array typically can be used if a uniform output is desired. This low efficiency of channel/waveguide usage results in large device size and lower production yield.